The FBI launched a 72-hour nationwide operation targeting pimps who prey on children — an undercover mission that rescued 105 teens ranging mostly in age from 13 to 17 years old, with the youngest victim being 9 years old, authorities said Monday.

‘Children with a void’

Ronald Hosko, assistant director of the FBI’s criminal division, said “Operation Cross-Country” — launched Friday — included sting operations in 76 U.S. cities that resulted in the arrests of 150 pimps.

Hosko said law enforcement refers to these young victims as “children with a void.” Once the pimp identifies that void and makes every attempt to fill it, a dependency between the child and the perpetrator develops, Hosko said. He added that the most vulnerable victims forced into sex trafficking range in age from 13 to 16. Most of the children come from either foster care homes or are considered runaways.

‘Cut across racial lines’

“This operation targeted venues where girls and adults are operated for commercial sex,” Hosko said, including places like street tracks, truck stops, casinos and hotels. “The victims cut across racial lines,” he said, and span all socioeconomic levels and demographics.

The FBI joined forces with 230 agencies around the country during the three-day mission, Hosko said. Every FBI field office in the nation was involved in the operation. “Operation Cross-Country” was the largest of its type and conducted under the FBI’s “Innocence Lost” initiative. The FBI said the campaign has resulted in rescuing 2,700 children since 2003.

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The Justice Department was running into immediate hurdles Monday in its investigation of possible civil rights violations by George Zimmerman in the shooting death of Trayvon Martin — namely, that after examining the case for more than a year, the evidence has not changed.

‘Racial bias’

Though the department announced after Zimmerman’s acquittal that it would consider a possible federal case, previously filed FBI documents show agents have not turned up any accounts that Zimmerman, before the February 2012 shooting, exhibited racial bias.

Attorney General Eric Holder, in his first post-verdict comments, confirmed Monday during a speech in Washington, D.C., that his department continues to investigate while signaling concern for the position of the Martin family and those — such as the NAACP — pressuring the DOJ. Holder even appeared to suggest the possibility of bias in this case, saying it’s important to address “underlying attitudes, mistaken beliefs and stereotypes that serve as the basis for these too common incidents.”

‘Number one challenge’

But Florida defense attorney Brian Tannebaum told FoxNews.com that the “number one challenge” for DOJ is the evidence, or lack thereof.

Still, the Justice Department agreed to requests from NAACP President Benjamin Todd Jealous and several lawmakers to keep investigating the defendant. The department is under heavy pressure from some groups to pursue the case further.

Was racial bias evident in George Zimmerman’s case? Feel free to share your thoughts on this issue!